This invention relates to an engine air cleaner that includes a porous perforate cleaning annulus, formed for example from pleated paper or felt. An annular air supply chamber surrounding the cleaning annulus is occupied by special baffles that impart a helical swirling motion to the dust-laden gas, thereby centrifugally forcing heavy dust particles to the outer area of the chamber. A scavenger fan draws the heavier dust particles from the supply chamber before such particles can migrate inwardly to the cleaning medium surface; the cleaning medium handles the lighter dust particles. A dust layer builds up on the medium surface at a relatively slow rate, thereby prolonging the service life and/or frequency of dust-dislodgement activity at the cleaning medium surface.